A NIHILISTIC PHILOSOPHY OF SCIENCE FOR A SCIENTIFIC PSYCHOLOGY?
Reply to Barrett on Jensen on Intelligence-g-Factor

Abstract

Barrett's (2000) nihilistic notion of the philosophy of
science is, I believe, very mistaken in its assumptions and
limiting constraints, which would be largely rejected by most
philosophers of science past or present. The conditions imposed by
Barrett would greatly hinder or even prevent progress in
understanding phenomena at the frontier of any relatively
undeveloped science, not only for psychology, but in any other area
of natural phenomena. The fallacy is in his assumption that we
cannot measure anything until we already know everything about what
we are attempting to measure. The history of every field of
science amply contradicts this Draconian restriction.

Keywords

behavior genetics, cognitive modelling, evoked
potentials, evolutionary psychology, factor analysis, g factor,
heritability, individual differences, intelligence, IQ,
neurometrics, psychometrics, psychophyiology, skills, Spearman,
statistics
1. The keystone of Barrett's (2000) philosophy of science seems to be
that all research, in order to be 'scientific' must be based on ratio
scale measurement, which measures an attribute in equal and additive
units on a scale with an absolute zero point that is perfectly
isometric with the attribute being measured. Ordinal or rank-order
scales, which constitute most of the measuring instruments used in
differential psychology, including IQ and most other tests of cognitive
abilities, are supposedly anathema to the advancement of science. Yet,
as far as I know, the stricture imposed by Barrett has not been
required for any other science. Many variables in the physical sciences
have been studied with well-defined but nonratio or nonadditive scales
- the hardness of gems, viscosity, and the refractive index. And many
'pure' or dimensionless numbers (as the correlation coefficient is) are
seen in the physical sciences, such as the ratio of electrostatic to
gravitational force.

2. In the history of measurement of certain properties, such as heat
and electricity, virtually nothing is known initially about the nature
of the property being measured. The early scales devised to measure
these phenomena were neither ratio scales nor isomorphic with the
property being measured. Temperature, for instance, was originally
measured by thermometers that were at best ordinal scales, and even
these had imperfect reliability in the psychometric sense. The kinetic
theory of heat was still in the distant future when the first
thermometers were invented. Does it make any sense to insist that
because scientists do not yet have a ratio scale for measuring
variation in some variable phenomenon X (in order to determine whether
it has any systematic relationship to a variable phenomenon Y), they
should be forbidden to determine whether there is a rank-order
correlation between the ordinal measures of variables X and Y? Would
such a correlation, if obtained, be scientifically meaningless?
Experimental manipulations of X or Y could further establish that they
have some common causal properties. Prohibitions of this kind of
procedure are certainly not recognized by Charles Darwin's statement
that "Science consists of grouping facts so that general laws and
conclusions may be drawn from them".

3. I grant that ratio scales can prove useful, indeed essential, for
answering certain questions in psychology, such as determining the
precise form of mental growth curves for various abilities. We can do
this, for instance, with reaction time (RT), which is a ratio scale,
but not with, say, spelling ability, arithmetic reasoning, or artistic
aptitude, for which there are no ratio scales, only ordinal scales.
One of the attractive features of RT with respect to g theory is that
ordinal measures of g are correlated with measures of RT, which may
afford the possibility of measuring g on a ratio scale. Because a
measure of RT based on any single elementary cognitive task (ECT) has
only a relatively low correlation with psychometric g, developing a
reliable and valid ratio scale of g based on RT would require an
optimal combination of various ECTs. We already know that RTs derived
from a number of diverse ECTs have multiple correlations with g factor
scores that approach R = +.70, even though no special effort has yet
been made to develop a battery of RT measures that might show even
higher correlations with psychometric g. Developing a ratio scale of g
based on time measurements may involve some mathematical tricks to
maximize the correlation of these measurements with psychometric g,
such as transformation of the scale, but this is a quite legitimate
procedure and is commonly applied in the physical sciences.
Psychologists are generally too reluctant to use transformations of
scale to permit their data to show a better or simpler fit to their
theoretical models. Normalized IQ scores are an example, based on the
theoretical conception that general mental ability approximates a
normal distribution in the population -- as do physical stature, brain
weight, and many other anthropometric variables.

4. In the course of the scientific study of a phenomenon, concepts or
theoretical constructs (such as g) typically 'grow' in definition,
complexity, and precision. These attributes are not all there at the
beginning, before a scientist is allowed to begin investigation, as
Barrett apparently thinks is necessary. The science of genetics affords
an example. Mendel, in 1865, explained the results of his simple
breeding experiments with peas in terms of 'factors' (the word gene
hadn't yet come into existence), about which nothing was known, except
that they served in Mendel's model as the cause of the observed
hereditary variation in a few specific characteristics of peas.

5. During the subsequent 88 years, Mendel's nondescript construct was
elaborated both theoretically and empirically. T. H. Morgan
hypothesized that genes are arranged on the chromosomes and, on the
basis of linkage analyses from breeding experiments with fruit flies,
measured genes' relative positions on the chromosome. (His ordinal
scale [in 'decimorgans' or 'centimorgans'] at the time would probably
have been unacceptable to Barrett.) Then H. Muller found that specific
functions of single genes could be knocked out or mutated by X-rays,
thereby further establishing their identity as molecular entities.
Finally, in 1953, Crick and Watson discovered the specific molecular
structure of the genetic code. (All of these scientists except Mendel
won the Nobel Prize for their contributions.) This chain of development
scarcely resembles Barrett's requirement that scientists must already
know the essence of what they are investigating and measuring before
they begin their empirical research.

6. Barrett is a recognized professional in the field of electro-
physiological research on psychological variables, particularly
relating certain brain variables, such as evoked potentials and nerve
conduction velocity, to mental test scores that strongly reflect
psychometric g. His empirical contributions in this field (some cited
in Jensen, 1998) depend on ordinal scales for measuring mental
abilities and, more generally, they do not in the least contradict the
psychometric methodology or the investigative perspective of the
research program illustrated in 'The g Factor' (Jensen, 1998, 1999).
Presumably Barrett now has in mind a new and improved scientific
methodology for the study of individual differences in behavioral
traits, particularly g, the earliest and now most solidly established
latent trait in the behavioral sciences. It will be interesting to
learn just how it differs from the investigative paths that have led to
our present knowledge about g.

7. As I am not an expert in the contemporary philosophy of science, I
asked two university professors, who are recognized experts in this
field and teach courses in it, for their opinions on Barrett's
position. I will only quote a few of their key points:

"Barrett's core error is not understanding the consequences of two
metatheoretic truths that all contemporary philosophers of science
accept, as far as I know: (1) Most theoretical concepts are defined
by their role in the conjectured theoretical network. (A subset are
'operationally' defined by a fairly direct tie to observations.)
(2) The theoretical network is incomplete. (3) It follows that
theoretical concepts are 'open', or what logicians call 'partially
interpreted'. Research continues precisely because they are open;
the research task is to 'close' them, although never completely.
Barrett ignores all this and seems uninformed as to contemporary
metatheory, especially the theory of implicit definition and open
concepts."

"As you surmise, Barrett's animadversions against psychometrics
apply across the board to all science."